PARIS — For the last few days, the Place du Palais-Royal, the gracious square abutting the Louvre in Paris, has been almost entirely occupied by a big black tent with a swoosh on the side and the words “We Run Paris” emblazoned on the front.

Officially the slogan for the 10-kilometer race through the city center that Nike organized on Sunday, it is also more broadly prescient, at least judging by what is going on in the upper echelons of fashion.

Where it increasingly seems like the variables of sport and street (themselves almost the same thing, as what is worn for sport is also worn all over the street) are running roughshod over the former sacred cows of couture. At this point, it looks less like a trend than a paradigm shift in dress.

You can understand it — there’s a reason activewear is everywhere, and it has to do not only with comfort, but with communicating a value system that prioritizes action over formality. And it is fashion’s task to reflect and respond to what it sees, or lag far, far behind. But every designer adjusts differently. And some better than others.

At Undercover, for example, it served as an easy base for Jun Takahashi’s riff on jazz, with the slouchy cargo trousers and striped tennis belts, floral golfing twin sets trimmed in ribbed knit, jewel-tone drawstring pants sporting (no pun intended) trombones, trumpets and treble clefs, and the needle-punched frocks that married military tailoring to album-cover-like silk screens. All worn with squishy sneakers and newsboy caps. If you’re team Sonny Rollins or Bill Evans, this was the look for you.